Problem
I'm trying to search for deleted pages, I realize there isn't a concept of this in MediaWiki, so I really am looking for deleted revisions in which the page itself is missing. The best I can come up with is something like this:
all: https://test.wikipedia.org/w/api.php?action=query&generator=alldeletedrevisions&formatversion=2&gadrdir=newer
search: https://test.wikipedia.org/w/api.php?action=query&generator=alldeletedrevisions&formatversion=2&gadrdir=newer&gadrprefix=T
but as you can see, it may or may not include missing pages.

Solution
Add a parameter of some sort that would query the revision table where ar_page_id cannot be JOIN'd (i.e. where the page is missing).